Vibration Measurement And Its Application Using Two-Wave-Mixing Interferometer

Vibration is one of the physical phenomena which commonly exists in natural world, production and life. The measurement of small amplitude, high frequency vibration and ultrasonic vibration is a very promising industry topic. Based on the photorefractive effect in bismuth silicate (BSO) crystal, an adaptive two-wave-mixing interferometer is built to measure the tiny piezoelectric ceramic vibration and ultrasonic vibration in this article.A dynamic holographic grating is formed due to the photorefractive effect when the reference beam and the signal beam interfere in the BSO crystal to give a distribution of light intensity. Because of the real time diffraction of reference beam and signal beam by the holographic grating, the energy transfer happens and the small phase modulation of signal beam could be demodulated to obtain the vibration signal.Sensitivity, the relationship between sensitivity and coupling efficiency, and the waveform distortion are analyzed through theoretical simulation and verified through experiments. A two-wave-mixing interferometer is designed and built, then some parameters are discussed to promote the sensitivity, such as the intense ratio, the total light intensity and the external high voltage on BSO. The experiment shows good coincidence between the theoretical model and real situation. Vibration of different frequency from 1 Hz to 800 kHz are measured to present the good performance of the system.The small pulse vibration of ultrasonic probe is measured successfully by this system, which matches with the result obtained by the ultrasonic probe itself. Then, the thickness of an aluminum block is calculated via the time interval of pulse traveling back and forth, since the ultrasonic vibration in aluminum block can be detected using our interferometer.